Intense pain in back while peeing please help

I've been having pains for a day or so now but it hasn't hurt to pee. This morning I peed and it was such a sharp pain in my left side, radiating down the back of my leg, j had to keep stopping and changing positions on the toilet. The pain was deep. It went away as soon as I was done and stood up. Does this sound like a kidney problem? (My left kidney is actually behind/in my pelvis) or could it be a bladder issue? Or just a nerve issue? I know my baby is super low. I'm at a loss and I can't see my ob until next week so my only option now is L&D if its a big deal, which is who I'd have to call and they don't tell you much over the phone so, because of the way they work. You have to come in and I don't want to if its nothing. I was having painful contractions yesterday that stopped and I am having some itching down there but it does away if I change my underwear so I assumed it's from a lot of discharge. I'm almost 35 weeks